Chapter 11 Chemical Reactions

Note Taking Tips! Paraphrase, paraphrase, paraphrase! Use symbols, arrows, pictures, and abbreviations whenever possible. Write side notes to help you remember concepts.

What is a chemical reaction? –Occur every minute of every day! –When one or more reactants change into one or more products. –Characterized by the breaking of bonds in reactants and formation of bonds in products

Law of Conservation of Mass In any physical or chemical reaction, mass is conserved; mass can be neither created nor destroyed

Chemical Reactions Chemical reactions are described by chemical equations. Skeleton Equation: chem equation that doesn’t indicate relative amounts of reactants and products. Fe + O 2 Fe 2 O 3 ReactantsProducts It needs to be balanced!!!

Draw this one It means the reaction is reversible

Catalyst: a substance that speeds up the reaction but is not used up in a reaction. –Neither a reactant nor a product –Written above arrow in chem equation. MnO2 H 2 O 2 (aq) H 2 0(l) + O 2 (g)

Balancing Act Bicycle scenario

Balancing Chemical Equations A chemical reaction where each side of the equation has the same number of atoms of each element and mass is conserved. Fe + O 2 > Fe 2 O 3

Steps to Balancing 1. Count atoms on each side. Count polyatomic ion as one unit if it appears unchanged on right. 2. Balance elements one at a time using coefficients –Balance elements that appear only once 1 st –Never change subscripts 3. Check work and make sure all coefficients are in lowest possible ratio. H 2 + O 2 > H 2 O

Let’s try some!

1._____ S + _____ O 2 --> _____ SO 2 2._____ Na+ _____ O 2 --> _____ Na 2 O 2 3. _____ Hg + _____ O 2 --> _____ HgO 4. _____ Ag 2 O --> _____ Ag + _____ O 2

Let’s try some!

Practice

11.2 Types of Chemical Reactions Concept map 5 general types –Combination –Decomposition –Single-replacement –Double-replacement –Combustion

Concept map instructions Get basic definition Write at least one chemical reaction Describe the demonstration reaction

Combination When 2 or more substances react to form a single new substance. 2Mg + O 2 > 2MgO

Decomposition When a single compound breaks down into 2 or more simpler products. 1 reactant, 2 or more products Usually require heat, light, or electricity to occur. 2HgO > 2Hg + O 2

Single-Replacement When 1 element replaces a second element in a compound. 2K + 2H 2 O > 2KOH + H 2 Look at the switch!

Double-Replacement An exchange of positive ions between 2 compounds. Usually produces one of the following –A precipitate –A gas –water Remember: positive ions=cations=on left side of a compound Na2S + Cd(NO3)2 > CdS + 2NaNO3 2NaCN + H2SO4 > 2HCN + Na2SO4 Ca(OH)2 + 2HCl > CaCl2 + 2H2O

Combustion When an element or compound reacts with oxygen, it produces energy in the form of heat and light. Oxygen is always a reactant The other reactant is often a hydrocarbon (something with hydrogen and carbon) –CH 4 methane –C 3 H 8 propane –C 4 H 10 butane –C 8 H 18 gasoline CO or CO 2 can also be products 2C 8 H O 2 > 16CO H 2 O

Practice!

Your Task Dissecting a chemical reaction